FIELD OF THE INVENTION
The present invention relates to an electronic sewing machine, and more particularly to a stitch pattern to be sewn to adjust the balance of fabric feeding amounts in the forward and rearward directions. With the development of an electronic memory for computer sewing machines which may store almost limitless amount of the data, it has become possible to stitch any patterns including very complicated patterns of a large number of the stitches formed in the forward and rearward fabric feeding directions such as alphabet letters, the images of flowers and animals etc.
The electronic control sewing machine usually stores, as pattern signals, a needle amplitude amount and a fabric feed amount for stitches which form patterns, and transmits said pattern signals to an amplitude control motor and a feed control motor. In this kind of sewing machine, a physical space within the mechanism for producing the patterns has more problems as the conventional pattern generation due to cams housed in the mechanical structure of the sewing machine. Therefore, it is possible to freely increase the number of the patterns stored in the sewing machine and the stitching number of the individual patterns. As a result various fine patterns or complicated patterns have been produced.
The mechanism of the electronic control sewing machine controls the forward feed and the rearward feed by reverse rotations around the control of the feed amount "0" of the feed control motor. The respective members of the feed control mechanism have manufacturing tolerances, so that a value of a signal indicative of the feed amount and an actual feed amount are more or less different.
Sewing machines were manufactured, where respective members of the feed control mechanisms were within the manufacturing tolerances. After their feed reference points have been adjusted, the actual feeding amounts were measured for the values of the signals of the feed amounts, and the relation therebetween was standardized, as shown in FIG. 1, in accordance with the measuring data.
As shown in FIG. 1, the broken line indicates that the feeding amounts and the feeding signals are in proportion 1:1 as desired both in the forward and rearward feeding directions. However, in the actual mechanism, the fabric feed reference point is to be usually unstable and is inevitably determined at a point on the lateral axis which is more or less spaced from the center 0. Thus if the feed reference point is once determined at a place other than the center 0, for example, on the plus side of the lateral axis, the forward feeding amounts will be constant with the respective feeding signals, but the rearward feeding amounts will be remarkably different from the forward feeding amounts even though the former may be constant in the rearward direction. This will considerably deform the patterns of the stitches formed with both the forward and rearward feeding amounts. In order to form the stitches of the same feeding amounts in the rearward feeding direction with the stitches of the feeding amounts in the forward feeding direction, it is necessary to displace the fabric feeding reference point to a place on the minus side of the lateral axis from the place on the plus side at the same distance from the center 0 as shown by solid lines in FIG. 1. Such a displacement of the feeding reference point is required each time the fabric feeding direction is changed during the sewing of a pattern.
Since the number of the patterns stored in the sewing machine and the stitching number of the pattern are increased, a first problem resides in that the existing adjustment is insufficient to regulate the feed reference point, and a second problem is that the existing pattern designing results in a big difference in shape between the data and the actual stitching pattern, and this fact could not be ignored.
The second problem could be solved in designing. That is, in the conventional method, the pattern was not stitched as requested by the signal as shown in FIG. 1, and such a difference was ignored. A model pattern was prepared as being stitched along the dotted line shown, and the feed amount signal was decided.
If the model pattern is simple and the stitching number is not many in the initial period of operation, the difference between the model pattern and the shape of the stitching pattern is not outstanding. However, as the stitching number increases and the model pattern becomes complicated, the difference between the feed signal value and the actual feed amount influences finished products.
This problem may be solved by distinguishing the signal in accordance with the standardized solid line in FIG. 1 from the model pattern when making the pattern data, and arranging that the model pattern and the stitching pattern be practically made of the same shape.
The standardization means such an operation which, in order to provide the same shape practically as described above, decides the quantitative relation between the value of the signal of the feeding amount and the actual feeding amount. In other words, the standardization means the operation which obtains relation between the measuring data of the actual feeding data and the value of the signal of said amount by a sort of a weighted average operation.
An outline of the feed control mechanism will be mentioned for explaining the above-mentioned first problem. The feed control mechanism especially controls the feed control motor in the forward feed and the rearward feed by rotations opposite to each other around the feeding amount "0". The feed control mechanism is, in a transmission path of the feed controlling amount, provided with a first feed controller for adjusting the feed reference point when the sewing machine is set up at the maker's side, and with a second feed controller which is set under the neutral condition of the operation when adjusting the feed reference point, and which may be operated from the outside of the sewing machine.
With respect to the adjustment of the feed reference point when the sewing machine is set up and regulated, the feed reference point is adjusted by operating the first feed controller. For this aim, the curve of the feeding amount as shown in FIG. 1 is determined for each of the sewing machines. Since it takes a long time for calculating the feed reference point, the feed control motor is firstly energized at the signal value "0" of the feed amount, and the actual feeding amount is set to be "0" by operating the first feed controller. However, since the actual feeding amount "0" has a width along the lateral axis as shown in FIG. 1, the controlling is still rough. Secondly several kinds of representative patterns are stitched, and the first feed controller is operated while observing finished stitches.
The representative pattern is such a pattern which is outstanding out of regularity if the feed refernce point is not correctly adjusted. A tulip pattern as one example is shown in FIG. 2. With respect to the figures 0, 15, 30 in the same, the full amplitude is equally divided into 30 parts and amplitude cordinates are set as 0, 1, 2, . . . 30 from the right. 0 is a right basic line, 15 is a middle basic line and 30 is a left basic line. The figure belonging to the pattern indicates a stitching number counting from a 1st stitch of an initial one. In this example, a discriminating portion is a distance between the stitches combining the 11th stitch--the 12th stitch and the stitches combining the 22nd stitch--the 23rd stitch. Since this distance is widened or draws "X" by crossing the threads, the adjusting condition of the feed can be discriminated while stitching the tulip pattern. However, 10 stitches are between the 12th stitch and the 22nd stitch, and these stitches determine the thickness of the tulip stem. As far as the electronic sewing machine forms simple patterns with lesser stitching number, there are not any special problems in the adjustment while stitching said representative pattern. The stitching number of individual patterns stored in the sewing machine has been increased, and the stitches of letters, characters or fine abstract patterns have been formed. Representative patterns have not been inherently prepared for adjusting the feed reference point. For abstract patterns, the shapes of patterns should be necessarily decided, taking aesthetic elements into consideration, and the abstract patterns may be used as the accidential result to regulate the feed reference point. The stitching number has not been sufficient for discriminating the adjusting condition of the feed reference point.
In the adjustment while stitching the representative patterns as conventionally, since the patterns are stored within the sewing machine, the stitched pattern is fed forward and under a presser foot, and fed in succession backward of the presser foot. Therefore, several patterns are stitched which are more in stitching number than the existing ones, otherwise the pattern is stitched and pulled out while stopping the sewing machine so as to discriminate the stitching condition by the present adjustment. It takes a long time for regulation.
Similar problems arise at the customers' sides where the adjustment of the feed reference point has been finished, but the balance between the forward feed and the rearward feed is temporally irregular due to quality of the fabric used or others.